JPH10247495A - Carbon material for secondary battery negative electrode, its manufacture, and nonaqueous electrolyte secondary battery using carbon material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery having a large discharge capacity and high charging/discharging efficiency and not deteriorating the cycle characteristics even when the charging/discharging current is a large current in particular by using a carbon material specified with the spin concentration, specific surface area, carbon lattice plane interval, and the size of a crystal in the C-axis direction for the negative electrode of the nonaqueous electrode secondary battery. SOLUTION: A carbon material having the spin intensity of 1×10<18> -3×10<18> spins/g at 25 deg.C, the specific surface area of 0.2-5m<2> /g, the carbon lattice plane interval d002 of 0.3354-0.3374nm, and the size of a crystal in the C-axis direction Lc of 50-2,000nm is used. Vapor phase epitaxy carbon fibers having the diameter of 1-4μm and the length of 3-30μm are preferably used. In manufacture, the graphitization process is applied to a raw material, then the high-shock process is preferably applied. The graphitization process is applied to the carbon fibers generated from the vapor phase for 30min at 2,800 deg.C in the inactive gas atmosphere. The carbon fibers are cut off by a hybridizer in the high-shock process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a carbon material for a negative electrode of a non-aqueous electrolyte secondary battery, a method for producing the same, and a non-aqueous electrolyte secondary battery using the carbon material.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries have been spotlighted in recent years because of their high energy density and excellent charge / discharge cycle characteristics, load characteristics, and safety. This battery is already expected to be in large demand for video cameras, notebook computers, mobile phones, and the like, and is expected to be applied as a battery for electric vehicles in the future.

In general, a non-aqueous electrolyte secondary battery has a configuration in which a positive electrode and a negative electrode are opposed to each other with a separator interposed therebetween, and these are immersed in a non-aqueous electrolyte. As this non-aqueous electrolyte, a solution in which a lithium salt is dissolved in an organic solvent is used. For example, a lithium-containing composite oxide is used for the positive electrode, and a carbon material is used for the negative electrode.

Examples of the carbon material for the negative electrode include graphite materials (natural graphite and artificial graphite), graphitizable carbon (vapor-grown carbon fiber, etc.), non-graphitizable carbon (PAN-based carbon fiber, etc.), amorphous Carbon (such as coke) can be used.
These carbon materials are usually used in the form of powder, but the shape of the powder may be particulate or fibrous. In addition, materials other than the above-mentioned graphite materials are used after being subjected to a graphitization treatment to some extent. This graphitization treatment is performed to grow graphite crystals in the carbon material by maintaining the carbon material at a high temperature.

In the non-aqueous electrolyte secondary battery, it is considered that charging and discharging are performed by inserting or removing lithium ions in the non-aqueous electrolyte between the carbon mesh surfaces of the graphite crystals. Have been. Therefore, if a large amount of lithium ions are inserted and desorbed between the carbon net surfaces in a large amount and quickly, the charge / discharge capacity becomes large. The percentage of capacity will be high. Conventionally, various carbon materials have been studied as negative electrode materials in order to further increase the charge / discharge capacity and further enhance the charge / discharge efficiency.

JP-A-6-73 filed by the present applicant
The graphitized vapor-grown carbon fiber described in Japanese Patent No. 615 is one example. This publication states that the diameter is 2.2 μm and the length is 1
4.6 μm, spin concentration 3.7 × 10 ¹⁸ spins / g
Describes the results of assembling a three-electrode cell using the graphitized vapor-grown carbon fiber of Example 1 and measuring the charge / discharge amount (mAh / g) and Coulomb efficiency (%) using the cell.

[0007]

However, the conventional carbon materials generally do not always have a sufficiently satisfactory discharge capacity. Moreover, among such carbon materials, those having the largest discharge capacity have a problem that the charge / discharge efficiency is lower than those having a smaller discharge capacity. Further, such a carbon material has a problem that the cycle characteristics are deteriorated due to low charge / discharge efficiency. The cycle characteristics tended to deteriorate especially when the charge / discharge current was large. Here, the cycle characteristics refer to the manner in which the discharge capacity changes when charge and discharge are repeated.

The present invention has been made in view of such circumstances, and has as its object to have a large discharge capacity, high charge / discharge efficiency even if the discharge capacity is large, and good cycle characteristics. An object of the present invention is to provide a carbon material for a negative electrode and a method for producing the same, in which the cycle characteristics do not deteriorate even when the charge / discharge current is large, and to provide a non-aqueous electrolyte secondary battery using the carbon material.

The present inventors have conducted intensive studies to solve the above-mentioned problems. As a result, if the number of unpaired electrons in the carbon material is large, the reactivity on the surface of the carbon material is activated. It has been found that lithium ions can be easily inserted and desorbed therein, and as a result, the charge / discharge capacity can be increased. On the other hand, the number of unpaired electrons in the carbon material can be known from the spin concentration measured by electron spin resonance analysis (ESR). The present inventors have reached the present invention by examining the relationship between the spin concentration of various carbon materials and the charge / discharge capacity in detail.

[0010]

SUMMARY OF THE INVENTION Therefore, the present invention according to claim 1 of the present invention relates to a method for preparing a carbon material used for a negative electrode of a non-aqueous electrolyte secondary battery using an electron spin resonance (ES) method.
R) is 1 × at 25 ° C.
It is characterized by being 10 ^{18 to} 3 × 10 ¹⁸ spins / g.

A carbon material having a spin concentration in this range is produced by subjecting a carbon material to a high impact treatment after a graphitization treatment. Also,
The carbon material has a specific surface area of 0.2 to ⁵ m ² / g and a carbon lattice spacing d _{002 of} 0.2.
A crystal having a crystal size Lc of 3354 to 0.3374 nm and a c-axis direction of 50 to 2000 nm is preferable.

The shape of the carbon material is not particularly limited, but is preferably fibrous.
As described, the diameter is 1-4 μm and the length is 3-30 μm
Is preferable.

[0013] The vapor-grown carbon fiber is produced by converting the vapor-grown carbon fiber produced from the vapor phase into an inert gas atmosphere at 2800 ° C for 3 hours.
Graphitization treatment is carried out by holding for 0 minutes, and then the carbon fibers are separated by a hybridizer for 10 to 30 m.
More preferably, it is subjected to a high-impact treatment in which it is cut by colliding at a linear speed of / sec for 0.5 to 5 minutes.

According to a sixth aspect of the present invention, there is provided a non-aqueous electrolyte secondary battery using the carbon material according to any one of the first to third aspects for a negative electrode. According to a seventh aspect of the present invention, there is provided a non-aqueous electrolyte secondary battery using a carbon material produced by the production method according to the fourth or fifth aspect for a negative electrode. These non-aqueous electrolyte secondary batteries can be manufactured by a conventionally known manufacturing method using a conventionally known material except that the carbon material of the present invention is used as a negative electrode material.

[0015]

Embodiments of the present invention will be described below in detail. First, the carbon material for a negative electrode of the present invention has a spin concentration at 25 ° C. of 1 × 10 ^{18 to} 3 × 10 ¹⁸ spins / s measured by electron spin resonance analysis (ESR).
g.

The carbon material for a negative electrode in this range has a large charge / discharge capacity and a high charge / discharge efficiency. The reason is considered as follows. The spin concentration indicates the number of unpaired electrons in the carbon material. Therefore, as the spin concentration increases, the reactivity on the surface of the carbon material increases, and as a result, the charge / discharge capacity increases.

When the spin concentration is less than 1 × 10 ¹⁸ spins / g, the reactivity on the surface of the carbon material is low, so that the insertion and desorption of lithium ions into the carbon material become inactive, and the charge / discharge capacity is reduced. small. In this case, when charging and discharging are performed at a large current value, the capacity is further reduced as compared with the discharge capacity at a small current value, and the cycle characteristics are significantly deteriorated.

Further, the spin concentration is increased to 3 × 10 ¹⁸
When the value exceeds spins / g, the reactivity on the surface of the carbon material is excessively activated, so that the carbon material is likely to cause a side reaction with the electrolytic solution. As a result, the charging / discharging efficiency is significantly reduced, and the cycle characteristics are accordingly deteriorated. Also, in the case of a battery using such a carbon material as the negative electrode, if an internal short circuit occurs in the same way as in the piercing test, the reaction with the electrolytic solution is activated, and the gas is rapidly decomposed by the electrolytic solution. Occurs and the battery may be damaged.

Among the carbon materials having a spin concentration according to the present invention, the specific surface area is 0.2 to ⁵ m ² / g, the carbon lattice spacing d ₀₀₂ is 0.3354 to 0.3374 nm, and the crystal size in the c-axis direction is It is preferable that Lc is 50 to 2000 nm.

When the specific surface area is less than 0.2 m ² / g,
In the case where the individual fibers or particles constituting the carbon material of the powder become too large, in this case, in the process of manufacturing the negative electrode, when the fibers are entangled with each other, or the surface of the particles is changed due to the size of the particles themselves. There is a possibility that the film may not be dense even if it becomes uneven, or is compressed by a roll press after being attached to the current collector.

On the other hand, if the specific surface area exceeds 5 m ² / g, the contact area between the carbon material and the non-aqueous electrolyte increases, so that the reactivity between them increases, and the irreversible capacity ( The difference between the charge capacity and the discharge capacity) increases, and the charge / discharge efficiency decreases.

The above d ₀₀₂ and Lc are values measured by the X-ray diffraction method. The case where d ₀₀₂ is 0.3354 nm is the case of a graphite single crystal, and is the minimum value of d ₀₀₂ . When d ₀₀₂ exceeds 0.3374 nm, the graphitization is insufficient, and the charge / discharge capacity decreases.

The case where Lc is less than 50 nm is also the case where graphitization is insufficient, so that the charge / discharge capacity is reduced.
On the other hand, when Lc exceeds 2000 nm, individual fibers or particles constituting the powdery carbon material become too large, and a negative electrode is produced as in the case where the specific surface area is less than 0.2 m ² / g. Can cause problems when doing so.

The carbon material of the present invention is preferably a vapor grown carbon fiber having a diameter of 1 to 4 μm and a length of 3 to 30 μm. This is because the vapor-grown carbon fiber is easily graphitizable carbon and has a very stable structure in which carbon net surfaces are stacked concentrically, so that a high cycle life can be expected.

However, if the diameter is less than 1 μm or 4 μm
In the case where the ratio exceeds 1, the graphitization cannot be sufficiently performed, so that the charge / discharge capacity decreases. In addition, the length is 3μ
If it is less than m, the specific surface area becomes too large, and therefore the charging / discharging efficiency is reduced as described above. Conversely, if it exceeds 30 μm, the individual fibers constituting the powdery carbon material are too long, and as in the case where the specific surface area is less than 0.2 m ² / g, when producing the negative electrode, Can cause problems.

In the case of producing the carbon material of the present invention, it is preferable to perform a high impact treatment after the carbon material is subjected to a graphitization treatment. What is important here is the order in which the graphitization treatment and the high impact treatment are performed. The material of the carbon material, for example, in the case of a vapor-grown carbon fiber, refers to a material generated from a gas phase. By this manufacturing method, a carbon material having a spin concentration within the range of the present invention is manufactured.

Further, in the graphitization treatment, it is preferable that the carbon material is held at 2800 ° C. or more in an inert gas atmosphere and the holding time is at least 30 minutes. However, even if the holding time is excessively longer than 30 minutes, the effect is not increased in proportion thereto. still,
As the inert gas, for example, an argon gas can be used.

The high impact treatment is a treatment for cutting a carbon material into an appropriate length with a high impact force. In this case, it is meaningful not only to shorten the length of the carbon fiber but also to expect that the internal structure is changed by making the end of the carbon fiber a cut surface and further giving an impact to the carbon fiber.

In order to apply this high impact treatment to, for example, a vapor grown carbon fiber, a hybridizer is used, and
It is preferable to cut the carbon fibers by hitting each other at a linear speed of / sec for 0.5 to 5 minutes. The linear velocity in this case means the linear velocity of the outermost part of the rotating blade in the hybridizer. However, cutting of carbon fibers such as vapor-grown carbon fibers is not particularly hindered by cutting methods other than such high impact treatment, and cutting by ordinary means such as a ball mill or stamp mill is also possible. is there.

Next, an example of the non-aqueous electrolyte secondary battery of the present invention using the carbon material manufactured by the above-described manufacturing method or the carbon material of the present invention will be described.

The non-aqueous electrolyte secondary battery of the present invention may have a configuration in which a positive electrode and a negative electrode are opposed to each other with a separator interposed therebetween, and these are immersed in a non-aqueous electrolyte. This non-aqueous electrolyte is obtained by dissolving a lithium salt in an organic solvent. As the lithium salt, for example, L
iClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF _{6 and the} like are used, and two or more of these can be used in combination.

Examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). It is also possible to use a mixed solvent composed of more than one kind.

The positive electrode is obtained by attaching a positive electrode material (positive electrode active material) to a current collector made of a metal foil. As the current collector, a belt-like aluminum foil is usually used. A mixture of a lithium-containing composite oxide and a conductive material as a positive electrode material is attached to both surfaces of the current collector.

Examples of the lithium-containing composite oxide include lithium cobalt oxide (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), and lithium nickel oxide (LiN
iO ₂ ) is used. The conductive material is added to increase the conductivity of the positive electrode active material, and for example, carbon black represented by acetylene black, graphite powder, carbon fiber, or the like can be used.

The lithium-containing composite oxide and the conductive material are usually used in the form of powder. These powders are mixed and dispersed in a binder solution, and the mixture is applied to the surface of the current collector. This is then dried and then compressed by a roll press or the like to form a positive electrode.

The binder solution is obtained by dissolving a binder (binder) in an organic solvent. The binder binds between the powdery lithium-containing composite oxide and the conductive material and between them and the current collector. As the binder, for example, polyvinylidene fluoride (PVDF) is used, and as the organic solvent, for example, N-
Methyl-2-pyrrolidone (NMP) is used.

The negative electrode is obtained by attaching a negative electrode material (negative electrode active material) to a current collector made of a metal foil. Usually, a strip-shaped copper foil is used as the current collector. The carbon material of the present invention is adhered to both surfaces of the current collector as a negative electrode material.

As the carbon material, a powdery material is usually used. The shape of the powder generally includes a particulate shape and a fibrous shape. The carbon material is generally used after being graphitized. Graphitization is a process in which a carbon material is heated to grow graphite crystals inside.

The powdery carbon material is mixed and dispersed in a binder solution as in the case of the positive electrode, and the mixture is applied to the surface of the current collector. Then, it is dried and then compressed by a roll press or the like to become a negative electrode. Also in this case, for example, polyvinylidene fluoride (PVDF) is used as the binder, and N-
Methyl-2-pyrrolidone (NMP) is used.

A strip-shaped microporous film is used as the separator. This film is made of, for example, polypropylene. A positive electrode lead is welded to the positive electrode, and a negative electrode lead is welded to the negative electrode. The positive electrode and the negative electrode are spirally wound via a separator, and the spiral positive and negative electrodes are housed in, for example, a cylindrical battery can. Then, the negative electrode lead is welded to the battery can, and the positive electrode lead is welded to the positive electrode cap. Next, the nonaqueous electrolyte is poured into the battery can, and then the positive electrode cap is crimped on the battery can to seal the battery can. Thereby, the non-aqueous electrolyte secondary battery is completed.

[0041]

EXAMPLES Hereinafter, the carbon material and the nonaqueous electrolyte secondary battery of the present invention will be described more specifically with reference to Examples. The examples are illustrative of the invention and do not limit the invention.

Embodiment 1 1. About carbon material (1) Production of carbon fiber A vapor-grown carbon fiber having a diameter of 2 μm and a length of 50 μm generated from the vapor phase was subjected to 2800 in an argon gas atmosphere.
Graphitization was performed at 30 ° C. for 30 minutes to obtain graphitized carbon fibers. This graphitized carbon fiber was filled in a hybridizer and subjected to a high impact treatment at a linear velocity of 20 m / sec for 2 minutes. The carbon fiber after the treatment has an average diameter of 2 μm, an average length of 15 μm, a specific surface area of 1.4 m ² / g, and a d ₀₀₂ of 0.2.
3361 nm and Lc were 100 nm.

(2) ESR measurement 4 mg of carbon fiber prepared in (1) and 100 m of potassium chloride
g was mixed in a mortar, and the mixture was filled into a quartz sample tube having a diameter of 5 mm and a length of 270 mm. After the sample tube was evacuated under vacuum, an argon gas was sealed therein and ESR measurement was performed. The ESR device used was ES-10 (a product name of Nikkiso Co., Ltd.). Magnetic field sweep range 335.5 ± 15 mT,
The magnetic field modulation was performed at 100 kHz (0.2 mT), the microwave output was 8 mW, the sweep time was 2 min, and the measurement temperature was 25 ° C. Table 1 shows the above results.

(3) Evaluation by Charge / Discharge Test First, in order to produce a three-electrode beaker cell, 0.1 g of PVDF as a binder was added to an organic solvent, NMP 0.1.
Dissolved in 8 ml. The carbon fiber prepared in (1) was added to
9 g was added and mixed well in a mortar. This mixture is 1 ×
After coating on a 5 cm nickel mesh so that the coating area was 1 × 1 cm, the coating was dried at 110 ° C. for 24 hours to obtain a working electrode. Using this working electrode, a counter electrode made of metallic lithium, and a reference electrode made of metallic lithium, a three-electrode beaker cell was produced.

The non-aqueous electrolyte used for this purpose is ethylene carbonate (EC) and diethyl carbonate (DE).
C) mixed solvent (EC: DEC = 1: 1, volume ratio)
LiClO ₄ dissolved at a concentration of 1 mol / l was used. Then, the current density was set to 25 mA / g, and a charge / discharge test was performed in a range where the potential difference between the working electrode and the reference electrode was 0 to 2.5 V. Then, the charge capacity, discharge capacity and charge / discharge efficiency in the first cycle were measured. Table 2 shows the results
And FIG.

Although the plotted points are connected by a straight line in the graph of FIG. 5, this means that the plotted points are simply connected for easy understanding, and that the plotted points are not necessarily linear. It does not do. This is the same in FIGS. 1 to 4 and FIGS.

2. Cylindrical non-aqueous electrolyte secondary battery (1) Preparation of electrode (a) Preparation of negative electrode 90 wt% of the carbon fiber prepared in (1) and 10 wt% of PVDF as a binder were mixed in NMP as an organic solvent, and this mixture was applied to a strip-shaped copper foil to obtain a negative electrode. (b) Preparation of positive electrode 90% by weight of LiCoO ₂ and 5% by weight of acetylene black
And 5 wt% of PVDF as a binder were mixed in NMP as an organic solvent, and this mixture was applied to a strip-shaped aluminum foil to obtain a positive electrode.

(2) Preparation of non-aqueous electrolyte EC + PC + DMC (EC: PC: DMC = 3: 3:
4, a volume ratio of LiPF ₆ of 1.2 m
The resulting mixture was mixed at a concentration of ol / l to obtain a non-aqueous electrolyte.

(3) Production of cylindrical non-aqueous electrolyte secondary battery After the positive electrode lead was welded to the positive electrode produced in (1) and the negative electrode lead was welded to the negative electrode, the positive electrode and the negative electrode were spirally wound through a polypropylene microporous separator. The spiral positive and negative electrodes were housed in a battery can having a diameter of 16 mm and a height of 50 mm, the negative electrode lead was welded to the battery can, and the positive electrode lead was welded to the positive electrode cap. After that, 2. The non-aqueous electrolyte prepared in (2) was injected. Next, crimp the positive electrode cap to the battery can to seal the battery can,
A cylindrical non-aqueous electrolyte secondary battery was obtained.

(4) Cycling Test of Cylindrical Nonaqueous Electrolyte Secondary Battery A charge / discharge test was performed up to 300 cycles under the following conditions.
The discharge capacity at the 100th and 300th cycles was measured. Charge / discharge current = 800 mA, charge / discharge voltage = 2.5-4.
1V. The results are shown in Table 3 and FIG.

(5) Cycling Test of Cylindrical Nonaqueous Electrolyte Secondary Battery at High Current A charge / discharge test of up to 300 cycles was performed under the following conditions.
The discharge capacity at the 100th and 300th cycles was measured. Charge / discharge current = 1600 mA, charge / discharge voltage = 2.5-
4.1V. The results are shown in Table 3 and FIG.

(6) Nail test of cylindrical non-aqueous electrolyte secondary battery A battery having a diameter of 3 mm and a length of 40 mm was charged at a speed of 5 cm / min into a battery charged to 4.1 V at a current value of 800 mA. Penetrated. At that time, the presence or absence of damage to the positive electrode cap of the battery was observed. Table 7 shows the results.

Embodiment 2 1. Production of Carbon Fiber A vapor-grown carbon fiber having a diameter of 1 μm and a length of 50 μm generated from the vapor phase was subjected to 2800 mm under an argon gas atmosphere.
Graphitization was performed at 30 ° C. for 30 minutes to obtain graphitized carbon fibers. The graphitized carbon fiber was filled in a hybridizer and subjected to a high impact treatment at a linear velocity of 30 m / sec for 0.5 minutes. The treated carbon fiber has an average diameter of 1 μm, an average length of 5 μm, a specific surface area of 4.8 m ² / g, and a d ₀₀₂ of 0.2.
3362 nm and Lc were 100 nm.

2. Measurement and Test Using this carbon fiber, ESR measurement was performed in the same manner as in Example 1.
A charge / discharge test, a charge / discharge test using a cylindrical nonaqueous electrolyte secondary battery, and a nail test were performed. The results are shown in Tables 1 to 3, Table 7 and FIGS.

Embodiment 3 1. Production of Carbon Fiber A vapor-grown carbon fiber having a diameter of 4 μm and a length of 50 μm generated from the vapor phase was subjected to 2800 g in an argon gas atmosphere.
Graphitization was performed at 30 ° C. for 30 minutes to obtain graphitized carbon fibers. This graphitized carbon fiber was filled in a hybridizer and subjected to high impact treatment at a linear velocity of 10 m / sec for 5 minutes. The carbon fiber after the treatment has an average diameter of 4 μm, an average length of 30 μm, a specific surface area of 0.9 m ² / g, and d ₀₀₂ of 0.2.
3363 nm and Lc were 100 nm.

2. Measurement and Test Using this carbon fiber, ESR measurement was performed in the same manner as in Example 1.
A charge / discharge test, a charge / discharge test using a cylindrical nonaqueous electrolyte secondary battery, and a nail test were performed. The results are shown in Tables 1 to 3, Table 7 and FIGS.

[0057]

[Table 1]

[0058]

[Table 2]

[0059]

[Table 3]

FIGS. 1 and 2 show the relationship between the spin concentration and the discharge capacity and the relationship between the spin concentration and the charge / discharge efficiency in the carbon materials of Examples 1 to 3, respectively. Also,
This spin concentration and 1 in the cylindrical non-aqueous electrolyte secondary battery
FIGS. 3 and 4 show the relationship between the discharge capacity at the 100th cycle, the 300th cycle, and the 300th cycle.

Next, for comparison with the above-mentioned examples, those not included in the scope of the present invention were produced and tested. Comparative Example 1 1. Production of Carbon Fiber A vapor-grown carbon fiber having a diameter of 2 μm and a length of 50 μm generated from a vapor phase was subjected to an argon gas atmosphere at 2800 μm.
Graphitization was performed at 30 ° C. for 30 minutes to obtain graphitized carbon fibers. The graphitized carbon fiber was filled in a hybridizer and subjected to a high impact treatment at a linear velocity of 40 m / sec for 10 minutes. The carbon fiber after the treatment has an average diameter of 2 μm, an average length of 5 μm, a specific surface area of 7.1 m ² / g, and a d ₀₀₂ of 0.3.
363 nm and Lc were 100 nm.

[0062] 2. Measurement and Test The carbon fiber is different from that of Example 1 in that the linear velocity in the high impact treatment is doubled and the time is five times. Using this carbon fiber, an ESR measurement, a charge / discharge test, a charge / discharge test using a cylindrical nonaqueous electrolyte secondary battery, and a nail test were performed in the same manner as in Example 1. A charge / discharge test at a large current using a cylindrical nonaqueous electrolyte secondary battery was omitted. The above results are shown in Tables 4 to 7 and FIGS.

Comparative Example 2 1. Preparation of Carbon Fiber Vapor-grown carbon fiber having a diameter of 2 μm and a length of 50 μm generated from a gas phase was filled in a hybridizer, and a linear velocity of 4 μm was used.
High impact treatment was performed at 0 m / sec for 2 minutes. This carbon fiber was graphitized in an argon gas atmosphere at 2800 ° C. for 30 minutes to obtain a graphitized carbon fiber. The carbon fiber after the treatment has an average diameter of 2 μm, an average length of 10 μm,
Specific surface area is 2.7 m ² / g, d ₀₀₂ is 0.3366 n
m and Lc were 80 nm.

2. Measurement and Test The carbon fiber differs from that of Example 1 in that the order of the graphitization treatment and the high impact treatment is reversed and that the linear velocity is doubled. Using this carbon fiber, an ESR measurement, a charge / discharge test, and a charge / discharge test using a cylindrical nonaqueous electrolyte secondary battery were performed in the same manner as in Example 1.
The nailing test of the cylindrical non-aqueous electrolyte secondary battery was omitted. The above results are shown in Tables 4 and 6 and FIGS.

Comparative Example 3 1. Preparation of Carbon Material Mesocarbon microbeads having an average diameter of 20 μm (specific surface area 0.7 m ² / g) were graphitized at 2800 ° C. for 30 minutes in an argon gas atmosphere.

2. Measurement and Test The carbon material is different from those of Examples 1 to 3 in that it is not fibrous but particulate, and that the high impact treatment is not performed. Using this carbon material, an ESR measurement, a charge / discharge test, and a charge / discharge test using a cylindrical nonaqueous electrolyte secondary battery were performed in the same manner as in Example 1. The nailing test of the cylindrical non-aqueous electrolyte secondary battery was omitted. The above results are shown in Tables 4 and 6 and FIGS.

[0067]

[Table 4]

[0068]

[Table 5]

[0069]

[Table 6]

[0070]

[Table 7]

FIGS. 1 and 2 show the relationship between the spin concentration and the discharge capacity and the relationship between the spin concentration and the charge / discharge efficiency in the carbon materials of Comparative Examples 1 to 3, respectively. Also,
This spin concentration and 1 in the cylindrical non-aqueous electrolyte secondary battery
FIGS. 3 and 4 show the relationship between the discharge capacity at the 100th cycle, the 300th cycle, and the 300th cycle.

As is clear from FIGS. 1 and 2, the carbon materials of Comparative Examples 2 and 3, in which the spin concentration is out of the range of the present invention, have a high charge-discharge efficiency of 92 to 93%. The discharge capacity was extremely low at 270 to 280 mAh / g, and the carbon material of Comparative Example 1 having a spin concentration outside the range of the present invention had a discharge capacity of 320.
Although the charge / discharge efficiency is relatively large at mAh / g, it is 82%.
% And extremely low.

On the other hand, the carbon material of each of the above embodiments is:
The discharge capacity is 320 to 350 mAh / g, which is larger than that of the comparative example, and the charge / discharge efficiency is 91 to 95%, which is sufficiently high.

As is apparent from FIG. 3, when the charge / discharge current is 800 mA, the cylindrical non-conductive layers of Comparative Examples 2 and 3 using a carbon material whose spin concentration is out of the range of the present invention are used. In the water electrolyte secondary battery, the discharge capacity at the first cycle, the 100th cycle, and the 300th cycle is as small as 760 to 770 mAh, 680 to 690 mAh, and 640 to 650 mAh, respectively, and the spin concentration is within the range of the present invention. Although the cylindrical non-aqueous electrolyte secondary battery of Comparative Example 1 using a carbon material that is deviated to a higher side has a large discharge capacity of 820 mAh in the first cycle, at the 100th cycle and the 300th cycle, 66 each
It is remarkably small at 0 mAh and 570 mAh.
This indicates that the charge / discharge efficiency is low and the cycle characteristics are poor.

On the other hand, the cylindrical non-aqueous electrolyte secondary batteries of each of the above-described embodiments have a charge / discharge current of 800 mA.
The discharge capacity at the cycle is as large as 820 to 850 mAh, and the discharge capacity at the 100th cycle and the 300th cycle is also 740 to 765 mAh and 720 to 750 m, respectively.
Ah and a very large value are maintained. That is, it can be seen that the cylindrical non-aqueous electrolyte secondary batteries of each of the above Examples have better cycle characteristics than those of Comparative Examples.

As is clear from FIG. 4, when the charge / discharge current is a large current (1600 mA), Comparative Examples 2 and 3 using a carbon material having a spin concentration outside the range of the present invention are used. Of the cylindrical non-aqueous electrolyte secondary batteries of the first cycle, the 100th cycle, and the 300th cycle have discharge capacities of 660 to 680 mAh and 480 to 500, respectively.
mAh, 290-320 mAh, and a charge / discharge current of 8
All are much smaller than the case of 00 mA, and this tendency becomes more remarkable as the number of cycles increases.

On the other hand, the cylindrical non-aqueous electrolyte secondary battery of each of the above embodiments has a large charge / discharge current (1600 m).
Case A) 1st cycle, 100th cycle, and 3
The discharge capacity at the 00th cycle is 800 to 830 m
Ah, 720-740 mAh, and 700-730 mA
At h, the same large value is maintained as in the case where the charge / discharge current is 800 mA. That is, it can be seen that the cylindrical non-aqueous electrolyte secondary batteries of each of the above examples exhibit extremely excellent cycle characteristics, particularly when charged and discharged with a large current.

Further, as is clear from Table 7, the cylindrical non-aqueous electrolyte secondary battery of Comparative Example 1 using a carbon material having a spin concentration outside the range of the present invention is the When the test was performed, gas was generated due to rapid decomposition of the electrolytic solution, and the positive electrode cap was damaged.

On the other hand, in the cylindrical non-aqueous electrolyte secondary batteries of each of the above examples, even when the nailing test was performed (as shown in Table 7), the positive electrode cap was not damaged. This is because the carbon material used in the batteries of the above embodiments has a spin concentration within the range of the present invention, and therefore has low reactivity with the electrolytic solution, so that gas is generated even if a short circuit occurs in the circuit. Because it is hard to do. That is, the non-aqueous electrolyte secondary batteries of each of the above embodiments have higher safety.

As is clear from FIG. 5, Comparative Example 1
The carbon materials of Nos. 1 to 3 have a discharge capacity of 270 to 320 mAh / g
On the other hand, the carbon materials of Examples 1 to 3 have discharge capacities of 320 to 350 mAh / g, which are larger than those of the comparative examples. Moreover, the carbon material of Comparative Example has a discharge capacity as small as 270 to 280 mAh / g (Comparative Example 2,
In 3), the charge and discharge efficiency is as high as 92 to 93%, but when the discharge capacity is relatively large at 320 mAh / g (Comparative Example 1), the charge and discharge efficiency is extremely low as 82%. On the other hand, the carbon materials of Examples 1 to 3 have discharge capacities of 320 to 3
It is 50 mAh / g, which is larger than that of the comparative example, and the charge / discharge efficiency is 91 to 95%, which is sufficiently high.

As is clear from Tables 3, 6 and FIG. 6, when the charge / discharge current is 800 mA, the cylindrical non-aqueous electrolyte secondary battery of Comparative Example 1 has a discharge capacity of 8 in the first cycle.
Although it is relatively large at 20 mAh, it decreases rapidly as the number of cycles increases, and reaches 570 mAh at the 300th cycle.
And becomes significantly smaller. The cylindrical non-aqueous electrolyte secondary batteries of Comparative Examples 2 and 3 had a discharge capacity in the first cycle of 760 to 760.
Since the discharge capacity is slightly smaller at 770 mAh and the discharge capacity decreases as the number of cycles increases, the discharge capacity becomes extremely small at 640 to 650 mAh at the 300th cycle.

On the other hand, the cylindrical nonaqueous electrolyte secondary batteries of Examples 1 to 3 had discharge capacities of 820 to 8 in the first cycle.
The discharge capacity at the 300th cycle is 50 mAh, which is larger than that of the comparative example, and the discharge capacity at the 300th cycle is maintained at a considerably large value of 720 to 750 mAh. That is, it can be seen that the cylindrical non-aqueous electrolyte secondary batteries of Examples 1 to 3 have better cycle characteristics than those of the comparative example (see the description of FIG. 3).

As is clear from Tables 3 and 6, and FIG. 7, when the charge / discharge current is a large current (1600 mA), the cylindrical nonaqueous electrolyte secondary batteries of Comparative Examples 2 and 3 have one cycle. The discharge capacity of the eye is 660 to 680 mAh, which is considerably smaller than the case where the charge / discharge current is 800 mA. When the number of cycles increases, the discharge capacity decreases drastically.
mAh, which is extremely small.

On the other hand, the cylindrical non-aqueous electrolyte secondary batteries of Examples 1 to 3 had discharge capacities in the first cycle of 800 to 8
30 mAh, which is considerably larger than that of the comparative example, and the discharge capacity does not decrease so much even when the number of cycles is increased.
The discharge capacity at the 300th cycle also maintains a considerably large value of 700 to 730 mAh. That is, it can be seen that the cylindrical non-aqueous electrolyte secondary batteries of each of the above examples show extremely excellent cycle characteristics especially when charged and discharged with a large current (see the description of FIG. 4).

[0085]

As described above in detail, according to the first aspect of the present invention, the carbon material used for the negative electrode of the nonaqueous electrolyte secondary battery is measured by electron spin resonance analysis (ESR). Spin concentration at 25 ° C. is 1 × 10 ¹⁸ to
Since it is 3 × 10 ¹⁸ spins / g, it has a large discharge capacity, high charge / discharge efficiency even if the discharge capacity is large, and good cycle characteristics. A negative electrode carbon material that does not deteriorate is provided. Therefore, the carbon material of the present invention
In particular, it is suitably used in applications requiring a larger current.

According to the second aspect of the present invention, the specific surface area is 0.2 to ⁵ m ² / g, the carbon lattice spacing d ₀₀₂ is 0.3354 to 0.3374 nm, and the crystal size in the c-axis direction is Since Lc is 50 to 2000 nm, it is suitable as a carbon material for a negative electrode having the effect of the first aspect of the present invention.

According to the third aspect of the present invention, since the vapor-grown carbon fiber has a diameter of 1 to 4 μm and a length of 3 to 30 μm, the carbon for a negative electrode having the effect of the first aspect of the present invention. It is suitable as a material.

According to the fourth aspect of the present invention, in the method for producing a carbon material used for a negative electrode of a nonaqueous electrolyte secondary battery, a high impact treatment is performed after the carbon material is subjected to a graphitization treatment. To have a large discharge capacity,
Even if the discharge capacity is large, a charge-discharge efficiency is high, and the cycle characteristics are good. In particular, it is possible to produce a carbon material for a negative electrode whose cycle characteristics are not deteriorated even when the charge-discharge current is large.

According to the fifth aspect of the present invention, the graphitization treatment is a treatment in which the vapor-grown carbon fiber produced from the vapor phase is maintained at 2800 ° C. for 30 minutes in an inert gas atmosphere. In the high impact treatment, the carbon fibers are separated from each other using a hybridizer for 10 to 30 m / sec.
Since the cutting is performed by hitting at a linear velocity of c for 0.5 to 5 minutes, the method is suitable as the manufacturing method according to the fourth aspect.

According to a sixth aspect of the present invention, there is provided a non-aqueous electrolyte secondary battery using the carbon material according to any one of the first to third aspects for a negative electrode.

According to the invention of claim 7, a non-aqueous electrolyte secondary battery using a carbon material produced by the production method of claim 4 or 5 as a negative electrode is provided.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a spin concentration and a discharge capacity in a carbon material.

FIG. 2 is a graph showing a relationship between spin concentration and charge / discharge efficiency in a carbon material.

FIG. 3 is a graph showing the relationship between the spin concentration of a carbon material and the discharge capacity of a cylindrical non-aqueous electrolyte secondary battery using the carbon material (when the charge / discharge current is 800 mA).

FIG. 4 is a graph showing the relationship between the spin concentration of a carbon material and the discharge capacity (when the charge / discharge current is 1600 mA) of a cylindrical non-aqueous electrolyte secondary battery using the carbon material.

FIG. 5 is a graph showing the relationship between the first cycle discharge capacity and charge / discharge efficiency of a carbon material, as measured by a three-electrode beaker cell.

FIG. 6 is a graph showing the relationship between the number of charge / discharge cycles and the discharge capacity (when the charge / discharge current is 800 mA) of the cylindrical nonaqueous electrolyte secondary battery.

FIG. 7 is a graph showing the relationship between the number of charge / discharge cycles and the discharge capacity (when the charge / discharge current is 1600 mA) of the cylindrical nonaqueous electrolyte secondary battery.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01M 10/40 H01M 10/40 Z

Claims (7)

[Claims] A carbon material used for a negative electrode of a non-aqueous electrolyte secondary battery has a spin concentration of 1 × 10 ¹⁸ to 25 ° C. measured by electron spin resonance analysis (ESR).
A carbon material having a density of 3 × 10 ¹⁸ spins / g. 2. The specific surface area is 0.2 to ⁵ m ² / g, the carbon lattice spacing d ₀₀₂ is 0.3354 to 0.3374 nm, and the crystal size Lc in the c-axis direction is 50 to 2000 nm. The carbon material according to claim 1, wherein 3. The carbon material according to claim 1, wherein the carbon material is a vapor grown carbon fiber having a diameter of 1 to 4 μm and a length of 3 to 30 μm. 4. A method for producing a carbon material for use in a negative electrode of a non-aqueous electrolyte secondary battery, wherein the carbon material is subjected to a high impact treatment after being subjected to a graphitization treatment. Production method. 5. The method according to claim 1, wherein the graphitization treatment comprises the step of: removing the vapor-grown carbon fiber produced from the vapor phase under an inert gas atmosphere.
The high impact treatment is performed by holding the carbon fibers at a temperature of 800 ° C. for 30 minutes using a hybridizer.
5. A process for cutting by hitting at a linear velocity of 0 to 30 m / sec for 0.5 to 5 minutes.
The method for producing a carbon material as described above. 6. A non-aqueous electrolyte secondary battery using the carbon material according to claim 1 for a negative electrode. 7. A non-aqueous electrolyte secondary battery using a carbon material produced by the production method according to claim 4 for a negative electrode.